Using 'this' in past tense

[Margo]

It's supposed to be told from 1st person POV, past tense. I keep finding myself confused about whether it's ok to use lines like, "Her nostrils flared and her lips tightened. I've never seen her so angry in my life." That's not a great example because it seems easy enough to change that one, but I've had other things like that come up where it reads fine as it is, but clearly it's changing up the tense. 1st person is harder in that way than I would have guessed.

I'm doing the same thing. I really got myself tied up in knots over a passage in past tense, talking about something that was going on prior to the scene, but on a continuing basis. A couple of the writers here had some fab suggestions for me, including some ideas on when I could just leave a sentence plain old past tense and let the context further define the relationship of events to one another.