I agree that it depends on the agreement. My T, for example, is fine with email at any time, though he usually replies in the mornings (including over the weekend). He prefers to only use texts for scheduling or for something really urgent (like a crisis). But I know some T's are fine with texting and might rarely use email.

So if yours seems like they'd be fine with it, and you think you'll be anxious about it all weekend, I think it would be OK to send a brief text. Though maybe wait until this afternoon (well, depending on your time zone!) to see if she gets back to you on her own. And I wouldn't expect a quick reply (or be concerned if you don't get one), as she could be busy with things.

Also, it's entirely possibly that she didn't get a chance to talk to her on Friday, so that's why she hasn't said anything. I know when my T was trying to talk to an ex-T, it took a bit of time for them to coordinate their schedules to find time to talk. So it may very well be that she hasn't been able to connect with her yet.