Juvenile spay is 4 months and under I believe.
Before first heat for your mix puppy is fine.
Feed well, exercise, keep her out of the sun for long periods of time without shade/protection from UV, away from lawn chemicals, PVC/vinyl is a good guess to avoid too, feed from quality metal bowls, tick and HW test yearly, train your dog well and happily, always safely contain her in the yard, on walks, in a vehicle, and in the house. - which also means safely containing your stuff, too
, make your vet your partner in your pet's health, do blood work before the spay, and when she's old enough to be a senior, yearly, do lump checks regularly, clean her teeth, spend time with her, and most importantly make sure she has good genetics (which we can't do or know with our mixes but we can always hope!).
I have a pre and post spay checklist when it hits that time if I don't see your thread, PM me.