Weather conditions over the past two years have been favorable for the production and survival of the food items of Common Tree Snakes. It would seem your friend is experiencing an influx of young dispersing CTS from somewhere nearby. As was mentioned, properly functioning window screens and weather strips on doors or self-closing security doors (fly screen plus mesh) are required to exclude them from the house.
Your friend is doing the right things. Those additional areas she could address are setting traps for rodents and looking at gardens and their placement, where frogs might reside. Bushy shrubs in a well watered garden bed are often a haven for frogs, particularly where hardcore chemicals controlling insect pests etc are not used. The proximity to the house will have a definite influence on the likelihood of snakes moving from outside into a house.
I believe it is a big ask of the un-initiated to expect them to be able differentiate between venomous snakes and completely harmless snakes such as the CTS. The rule of thumb should be to always be to treat any snake as a potentially dangerously venomous visitor unless you are competent enough to positively ID a species with 110% confidence.
Hopefully there some information of use there for her.
Blue