Help managing new behaviour of 3 year old daughter.

My daughter, over the last 2 weeks, has started crying when we ask her to do certain things. She is 3 years old and has very good language and comprehension skills, but for some reason just lately, whenever we tell her it's time for a shower or that we need to brush her teeth, she starts crying in an almost hurt very distressed manner. Nothing has changed, we have always had a routine of dinner, shower (with me) and in the shower we brush our teeth; she does hers first then I follow up brushing them for her. Then one night she refused, but I talked her around and we followed our usual routine, the next night it was tears and on for young and old. And ever since she won't let me near her teeth. She will let her father though, which is what we have been doing, but is very frustrating. She also decided last week that she wanted to shower on her own; this I get as she has had a growth spurt lately and there really isn't enough room for both of us if she wants to play in there.

There have been other occasions when she crus like this as well, but the brushing of the teeth is the main ongoing one. When she cries, it's like she's trying to hold it in but the emotion gets too much and she starts sobbing. Any parents out there have any suggestions as to how to approach this behaviour, I'm stumped, my very agreeable little girl who you could reason with has had a complete change in behaviour. Help please!