If I were in the daughter's shoes I could never trust anybody ever again, not even my future partner.
Besides that, just think what if the daughter starts doing the same things when she grows up.
It's like teaching your children the wrong things because they learn only from their elders.
You know if you want to take to that extent of not trusting anyone then you could be having issues in business because of trust issues. I won't say the daughter shouldn't trust anyone but it's also important to mind how we do put our trust in people because at any time they can change without you noticing or having to understand that they have already changed.
You are right because even though people cannot be trusted but we should not learn the habit of not trusting anyone because you can end up living a lonely and sad life because you will basically be having trust issues with everyone around you even when they have genuine intentions. We should still learn to trust people but not trusting them too much so that when they betray us, it will not affect our mental health. If you can't trust people, it will even be difficult to have a partner because where there is no trust, there will be no love.
Lot of people with whom they always confide on and even if people aren't trustworthy enough there is someone out there to be at least having that trust, and as we know trusting people seems to be very difficult especially when something unimaginable has happened to you and you would be looking for a possibility to blaze and cheer up without having that recurrent thinking within yourself that you have once lost a trust in people. We should always have this at the back of our minds that humans can change at any given time and we can't solely defines how they could be for long run, like I do say even myself at most can seem to trust myself but most times there are some tempting situations where you wouldn't know what transweird between you and the next person but you would noticed that you are longer that secure with someone whom you might be confiding on for long term due to little lapses or compromise.