I would work on my communication of my processes including letting them know asap of their schedule with me. 

Assuming you already paid for the first occurrence, if it happens again and the plumber doesn't find anything wrong then, yes, the tenant should be responsible for the invoice.Your PM should be setting those expectations when they communicate with your tenant."

Do not communicate with the tenants except as advised by the attorney.

There has been quite a bit of complaints in the past year of IHA mishandling payments or not paying at all and little to no communication.

On the other side, the bigger companies have more experience and their numbers tend to be more accurate (not always)... as they are big companies "their costumer service" and communication is better but at the same time they "have more mouths to feed" if we need to be honest so can get a bunch of ok or good deals but I kinda doubt they will be great (just my personal candid opinion).

Building trust can lead to better negotiations and more opportunities in the long run.Managing seller relationships is about clear communication.

Be responsive, communicative, deliver on what you say you are going to deliver (e.g. photos are true representation of your properties, amenities reflect what you actually have).  

For this situation, communicate very clearly and bluntly with the tenants and try to realign expectations so they don’t do this same with you.

I'd recommend communicating more with the PM directly.

You probably had a gut feeling when you first approved her, but you hoped it would work out.Stop communicating with her.