We have a non-jewish babysitter for our daughter. To avoid many issues we bought her a microwave specifically for her. I don’t know for sure, but I’m assuming that non-kosher food has been warmed up in it. If she used a Pyrex measuring cup to heat up water in that microwave is that cup now treif? Do we have to Kasher it? The microwave is kept very clean.

Shalom, If the microwave was indeed clean from any non-kosher foods or remains, then the Pyrex cup is kosher. (We rely, jointly, on the opinions that say Pyrex glass is non-absorbent and the opinions that say microwaves do not transfer taste to vessels heated up in them - though if only one of these factors was present the ruling may be different). Blessings, D. Sperling.