Suggestions for how to get around this?

I live with my S/O and his parents. SIL is here for a few months with her kids. She has a rule where you have to shower and wash your hair after work and being in a store or you can’t be around the kids.

My MIL and FIL follow this rule even though they feel changing clothes is enough.

I’ve been out of work but plan to go back before their leaving and I’m not about to wash my hair every day because it ruins it. I’m fine showering for them but that’s it.

Any suggestions for getting around it? The bathroom is shared and not attached to our bedroom so I can’t just pretend I’ve washed and blow dried my hair. I have to physically leave the bathroom which is near the main living area and walk into the bedroom to get all my stuff to blow dry my hair.