Kristin, hun, I would not discount the nanny option because of this incident.
The reality is that you are the best person to look after your own child. The reality is that something can happen to your LG regardless of where she is without you. You need to do your homework - regardless of which option you choose. A psychologist who specialises in family trauma told me that he often has to see children who have been abused in a creche environment.
Emotional abuse, or neglect or physical or sexual abuse can take place anywhere. I personally am terrified of not knowing where my LG is the whole day, or - more importantly to me - who she has been exposed to during the day. A scary thought that occurred to me recently is, yes people ask about the carers at schools. But what about other staff eg cleaners or gardeners? Who screens them? How do you know what could happen to your child alone for even 5 minutes with a trusted neighbour even? The reality is that these things can happen no matter what steps you take to prevent it.
However, it is up to you - as parent - to do your damndest to prevent it. You need to be vigilant, you need to do your research, you need to do your homework. You need to put in the time. It is your job. Finding an environment you feel is comfortable and safe for your child, is not the same as looking for a garage to service your car. You need to put in the time.
Finding someone to look after my LG while I'm not there was a very very painful experience. I went through 5 nannies before I found THE ONE. I interviewed at least about 20 before I decided to try the rest. Yes, I paid R2,500 upfront to find that nanny. But R2,500 paid to an agency vs what can happen without the screening process? No contest.
I also spent 2.5 months at home every day with the nanny before I trusted her alone with my precious LG for one day. She got to know me, I got to know her. We are like sisters and I wouldn't have it any other way. But make no mistake, I wasn't then nor am I now naive or complacent. I know it is my job to make sure my nanny is kept happy. If she is happy - genuinely happy - she will look after my LG in the best way.
I also check in unexpectedly so I know what is going on in my home. One has to be realistic about these things.