The runaway characters (Lisa, Kasumi, Ayane) I really hate online, it's such a bastard to try to get in their face and they can just hammer out strings that should be punishable but of course aren't. Helena is a similar story. Someone suggested more qcf+p to get in and I can't argue with that but I need to try it out. Turns out my joystick has a known issue with not hitting diagonals though so I'm not going to be online til my JLF shows up and I swap it out, so I can't say if that's good or bad advice. Not worth playing not being able to hold high against mashers; I've been losing to some embarrassing shit between the stick issue and the lag. Online in general tilts the playing field against grapplers, as the tradeoff for being faster in the striking game for most characters is having to be more careful about leaving themselves open to the big throw punishes of the grapplers. That is so much harder online, so it's a hold game defensively. Tina's not bad at that (oh, do mid kick me, please?), but she's sure not Bayman.
My general strategy against anyone is to stay as far back as I can safely land 6f+k or 46p and 46f+p, and try to get a knockdown somehow (typically 6f+k into ground throw) or start a combo with CH 3k/hold 3p or 44p, rarely 1k. Crouch dash to JO cyclone can catch them napping sometimes, and you can pressure with 46p or 7k guard breaks if they really turtle up. She needs to stay in that sweet spot where she can threaten effectively but isn't going to just get jabbed out of everything. Once you've got the knockdown your shitty speed in the striking game is mitigated somewhat, it's a lot easier to pressure a teching opponent. Or you pray they're dumb enough to rising kick and either block and throw the low rising kick or advanced mid kick hold the mid rising kick to get backturned into possible death. You don't want to rising kick Tina, well, ever. I don't think this really changes against a grappler much other than you can afford to close in and pressure a little more. Defensively, I would say block and punish but that never works very well at least online. While I hate to fall back on 1p I have to admit 1p to a mid/JO cyclone mixup can be damned effective. Also, 46p ducks highs basically instantly, so if they're coming in with high strings you can pick them out of that. Also works if you're in their face and you see a jab coming.
As far as starting stun on NH, Tina's actually got some decent options, they just tend to be slower/unsafe. Fastest is 4k at 14 frames, but it's not only throw unsafe but back throw unsafe. You might be able to get out of it if they get greedy (it's only -7) but if they're smart you're going to take damage on block. 9p is the next best option, it has followups and I believe it tracks but of course hits high and is 15 frames. Can't see 9k being useful unless it tech jumps? 44p is good, tech crouches, is technically unsafe, but has good followups so it's a little less likely they'll just bust out the throw on reaction. Of course there's 6k and 66k, but they are pretty slow.
Don't forget you've got some good options to force a normal throw (and if you're going for a throw naked you might as well go for 41236f+p or something nasty). pp gives you the threat of the k followup, pk or k gives you the threat of the p followup. Don't discount the damage you can get from a simple pkk or kk, either; if it goes right you can get close to 90 damage, and that ain't nothin; the opponent has to respect the p follow up as well due to possible limbo stun, so getting cute with ducking and low holds isn't necessarily the best idea. 3k and hold 3p both have solid mid followups. Also, 3k is totally safe and hold 3p is a 12 frame mid that ducks highs, that helps a lot. I've been trying to incorporate more crouch dashing to set that up in my game, also since that sets up JO cyclone/MDT; you can do a quick tap of f to guarantee you get hold 3p or 3k rather than 33p or 33k instead. Properly spaced, 66pp is a natural combo even on block, so you may be able to exploit people trying to hold the second p and getting delayed into a hi counter throw, I haven't played with this enough.
Inside stun, the stuns from hold 3p/BT 4p, 6p+k, and BT 7k / 66k give you relatively safe throw opportunities even if you whiff, and at least BT 7k/66k will give you a ground throw if the opponent doesn't tech when they fall down. They'll stay standing if they hold. But you know what to do then. There's of course the classic Bayman tactic of timing OHs to hit right out of stun recovery. I think that might work well with the power blow available as you may be able to mix up 1p+k and 46f+p; the charging animations are similar enough that it's not a horrible mixup, and the two moves have different timings so you may mess up hold/low throw attempts if you vary the charge. It's not even a bad tactic without the power blow. But a +17 guard break or 80 damage is a much better result.
If they're guarding, Tina's got some guard breaks to go around. Properly spacing 46p is probably her best one against Bayman and Bass, since she's as fast or faster than they are; even if you're blocked at +0, you're not at disadvantage, and at +2 you should be able to 6p freely. Against a faster character you may be forced to try to trade jab with mid or tech a jab with 1p, 3p or 46f+p even at +2. There's always sidestepping too. On hit you can get free ground throw if you run up and they don't tech or have a shining wizard/whatever mid mixup if they do. Same idea with 3p+k or 66p+k, though the latter is much harder to space appropriately and you might end up at -2. 7k is the best guard break against anybody, as you should be able to use 46p, 44p, or 6f+k freely, or use 66f+p to beat any high/mid attack. 7k is slow but surprisingly good against turtles. 1k is not technically a guard break, but on even NH unless they are god of stagger escape you should be at least at +3 and crouching, so hold 3p should beat anything and JO cyclone is on tap; sucks to be blocked, of course. And of course the power blow is the best possible guard break. Tina has a better option to throw it out naked than most given 46f+p as I mentioned earlier.