If you have your own mum to take care of baby at least till she's about 3 years old or so, will you continue this arrangement or send your baby to school earlier. Why and why not?

Depends. If your relationship with your mom is good and you are happy with her childcaring method then good to leave the child with her until a certain age. 18mo can send to half day playground already, your mom can send the child there so she has some sort of break in between.