Just use good judgement. Remember you are bringing the mother back into work, slowly, and that the foal will need to nurse.
This wasn't a problem for T, we rode in the arena and Walka followed his momma. He was a nosey little bugger and I didn't want to alarm his momma by taking him out on the trail until we had a bit more handle on things. He would let me know when he needed to nurse. It was a gradual process, like everything.
I will caution you however of stepping it up too soon for both mare and foal. An experienced horsewoman in my club, who should have known better, took a foal on a long trail ride. When we finally stopped for lunch and a rest , that foal was showing signs of exhaustion. We spoke with her and were able to convince her to take a shorter route back to the trailers with another rider for the foals sake. Was it's first outing! Sometmes people get too comfortable with what they think they know.
Glad you're asking for input, and I'm sure you'll get more.
Be the kind of woman that when your feet hit the floor each morning the devil says, "Oh crap, she's up!".