Very typical at this age. Kids at 4 start to resist all kinds of things -- they realize that the bath that was such fun a few weeks or months ago is eatiing up precious time they want to spend doing something else. Anything else. It's the same mentality that makes them scream that they don't want to come inside after being outside; they don't want to go outside when they're playing inside; they don't want a play date to end; they don't want to get in the car; don't want to get out of it....Whatever they are doing (or just sitting there thinking) is more interesting in that particular second of time than what you want them to do. The fact that she's happy once the BATH becomes the interesting, fun thing shows that the problem isn't that she fears baths for some reason -- the problem (to her mind) is that in the moment you say "bath now" her brain and attention are focused elsewhere.
This is a time just to be calm, calm, calm and consistent. If you make it a battle and yell or punish, she will "get her back up" as my mom would have said and will resist harder night after night because (a) she's learning to push your buttons; (b) the more you want it, the harder she'll fight it; (c) did I mention those buttons?....Don't force her into a tub if she is literally kicking and screaming, because that is unsafe for you both, but do make it calmly clear that NOTHING else happens until she is in the tub.
Once she's there you can try some new things like reading a brief story while she's in the tub if she loves those, but do still give consequences if she fusses. Keep them immediately connected to what's happening (it does not help a kid this age learn anything if you take away something the next day -- she won't fully connect what she did tonight with a consequence more than 12 hours later).
This does pass but you may find her resisting other things you ask (or tell) her to do for several years. I found that ages three to about six were tough years for getting kids to break from doing things to move on to a new activity, especially one seen as a chore by them. Not letting it become a fight every time is very important. Keeping your temper and being consistent is key too. If the baths are not daily maybe they should be -- but much shorter? Then she knows to expect them every time, instead of being surprised when it's tubby time and she thinks "LAST night there wasn't any tubby time! Why tonight?!" And she will indeed still be surprised in HER mind even if you told her two hours ago she had a bath coming tonight; her brain is in the moment. I'd give a one hour notice, a half hour notice, and then notice every five minutes starting 15 minutes before a firmly set tub time.