Is it permissible for my sister to pray in clothes stained with impure blood, given that she works in a clinic and has no place to change her clothes, and she is compelled to do this work?

For the prayer to be valid, the body, clothes, and place must be pure from impurities. If blood gets on the clothes, they must be purified, and prayer is not valid with them. A female worker in a clinic can change her blood-stained clothes in the women's restrooms into pure clothes. One must not be complacent in this regard, nor delay the prayer from its time, nor pray in blood-stained clothes as long as clean alternatives are available. If she cannot find any clothes other than these impure ones, or if there is no place to change, then she should pray in her impure clothes and not delay the prayer.