As wing chun practitioners we train a lot to fight people larger than us, however that doesn't seem to apply very well when it comes to people who grapple well.
What things do you do to prepare for people who are larger and/or better grapplers?
Part of the problem here is revealed in your other post about a sparring partner grabbing your wrists and shoving you around.
The problem is the tension in your arms and shoulders.
If someone grabs your wrists they may (momentarily) have control over your wrists but you should not give them control over the rest of you. If your shoulders are tight, your rigid arms will be levers with which your opponent can pry your body off balance and then push you around with them. At the other extreme, if your arms are floppy loose, there's nothing stopping your opponent from letting go of your wrists and striking.
Your SLT and chisao should develop a flexible tension that oozes forward like an inflating balloon. When your opponent grabs your wrist don't overreact, she'll be waiting for that. Your forward tension (coupled with a good root) will make it hard for her to disengage without creating an opening for you to strike. If she shoves or pulls, use that movement to initiate whatever technique you use to break the grip.
Now with regard to grapplers...
I believe from a woman's self defense standpoint, your should be less concerned with someone shooting for a double leg takedown as you might see in the ring, and more concerned with someone grabbing your arms or upper body to take you down.
Now the same principle applies. They need to get a meaningful purchase on you...stiff arms would be giving your assailant exactly what he needs.
Its just an idea which underlies any technique you choose to use in practice against those you want to grapple you.
I hope you find it reflects what your sifu has been teaching. Good luck in your training!