sorry to hear things are going so poorly....hang in there. First, if you've just returned from being gone, that will definitely mess things up, but since there were problems before you started, let's not wait to see what we can do....
Normally, with a 30 min nap, I'd say she' overtired, but maybe you're right and she's actually undertired. Do you know that she wakes at 5:30 - is that when you go in, or do you just hear her on the monitor? Also, at this age, I notice that my dd's "tired" cues are usually just "I'm bored" cues...so I tend to go more by the clock. Your routine actually looks pretty good. It's possible that she's OT from the travelling, so maybe pull back 15 min on her am nap and see what happens - try putting her down at 8:15 if she's up at 5:30. If you're still getting a 30 min nap, I'd go the opposite direction and try to add 15 min (putting her down at 8:45 if she's up at 5:30). Sometimes it really is a bit of flexible A time to try to find the right "fit" for your lo.
If she doesn't nap well, I'd still try to keep her up for awhile longer before putting her down for her next nap. So maybe if she goes down at 8:15 and wakes at 8:45, try to extend her maybe til 9, then just get her up, have some low key A time, feed as usual (solids and milk), and try to put her down around 11:30. I'm not sure if that will work though, depends on how tired she's acting (keep in mind she may be bored when she seems tired).
I'm sorry this is so hard. Each lo is different, so we just have to try to find the right bit for you lo. Hang in there!!!!