Random diaper rashes?

My one year old daughter has gotten the occasional diaper rash throughout her first year of life but nothing a little bit of rash cream can’t fix. However, recently she has been getting them so often, about once a week. They range from mild to severe. We haven’t changed the brand of diapers, body wash or anything. Today she was completely fine then while we were out running errands she fell asleep so there was about a 2.5 hour gap where her diaper was not changed and to my surprise she had a pretty moderate rash on her bottom.

Any ideas as to what can be causing this? I was thinking maybe the friction with her diaper because she’s walking now? I literally have no clue.