My children are stronger in French but never use it with me. My dh doesn't speak English and I lived and worked in France before meeting him. Our kids only use English with me.
If they are frustrated, mad or whatever, they speak to me in English.
Out in the community, I use English with my kids. It's not rude. It's not awkward. Sometimes we're mistaken for tourists but at the school, with friends, family, etc. they're used to hearing our exchanges in English. We never hold big conversations with others present who don't understand and most of the time, people can tell that our exchanges are super-banal and/or obvious (chasing a toddler on a cold day with a winter coat, who needs a translation??)
Once, my son came up to me at a music show his sister was participating in and protested "I'm BORED!" Everyone around us broke up laughing. The woman next to me who doesn't speak English quipped that no translation was needed that time.
Your child will quickly figure out which language she can use with you. If you use the excuse that you're "in public" or let them recount entire sentences to you in the community language, you're on a slippery slope towards the child only understanding the language. If she can get her needs met with only one language, why should she bother? This is the moment to hop on this and to make sure that the way to communicate with you is in French.
Understanding, but not speaking, French wont do her much good in the future. She can't participate in family functions. She can't put it on a resume. She wont feel a part of the culture. Speaking is the difficult part, but is far easier as a child who can pick up the accent than attempting this as an adult. Anyone can understand a language. It's speaking which is the "real" skill.
Don't make it a battle. There are some norms that she's getting to know, including using the potty and not hitting on the playground. Just make this a standard, not a debate.