If she is returning tomorrow, it's perfectly fine to send her a text now. Waiting for her to return might be a good idea if her vacation is long, but in this case, she will be back soon, so there's no harm in reaching out. A simple text to say something like, "Hey [Her Name], I hope you're having a great time on your holiday! Looking forward to catching up when you're back. Safe travels!" can be a friendly and considerate gesture.
Keep in mind that everyone's communication preferences are different, and some people might appreciate a message while on vacation, while others may prefer to relax without any distractions. If you know her well enough, consider her personality and preferences before reaching out. If you're unsure, a friendly message expressing your excitement to catch up once she's back should be well-received.
Also, be understanding if she doesn't respond immediately upon her return, as she might need some time to settle back in and get back to her regular routine. Patience and respect for her time and space will go a long way in maintaining a positive connection.