While I still think it is weird not to have reported her missing sooner...she is/was 23, a full-fledged adult, not a child or even a vulnerable teen. If her mother(s) did not find it that unusual for her to be out of touch for 3-4 days, why should anyone else? And HF may have his own reasons (arguments, etc.) for assuming she just took off for a few days.
My sisters and I have an agreement that if they can't make contact with me over a 24-hour period, they will call my apartment manager and then two close friends whose numbers I have given them. But that is because I am in a city with no relatives, live alone, and have a very orderly routine life.
When twenty-somethings can't be reached, and no one panics, I have to assume it is not that unusual. Jmo
I agree it's not that odd when a young adult is out of touch for several days; however, if I was trying to reach someone and it was obvious their phone was dead or turned off (went straight to voicemail) for several days in a row, I would most likely be concerned enough to start checking with the person she lived with just to make sure all was well. If her phone was ringing and going to voicemail, I probably wouldn't be all that worried. JMO