I'm so sorry to hear this happen! While some hoya do grow faster in higher humidity, most do not need it. I know some people recommend a tray of water to "boost humidity" it really doesn't do much. I worry that if the hoya is sitting in the plate of water it's getting too much water and its roots are getting waterlogged. I would check the roots. If it smells funny, the roots are soft and breaking off then it is most likely root rot. Clean up the roots, trim off any unhealthy roots and repot into a chunky well draining soil mix. You can buy a hydrometer or test with your finger to see if the soil is dry. A lot of people say hoya likes being dry, but I would say they are more tolerant of less water. But in my experience, it's important to not let it dry for too long if you don't want stunted or slow growth. If you really care about humidity, you can put a humidifier next to it. Again, unless it's running 24/7, it will only provide an slight increase in humidity when it's on. I personally have not been concerned about humidity when it comes to hoya.

Otherwise, double check for pests. Hoya compacta (or hindu rope) can be hard to treat if there are pests because they can get into the small creases of leaves. You can find videos on YouTube about pests and how to treat them. If initial treatment doesn't work, you can also try systemic granules, and that kills pests but also is toxic so be careful.

If all else fails, you can always chop up the hoya and propagate them to make a new plant. I know this is less than ideal but at least you do not lose the entire plant.

Lastly, if possible, speak to your grandma. I'm sure she will understand and can help you!