Baby scratching face

My daughter is almost 6 months. I always keep her nails down because she still occasionally scratches her face. Today I got her up from her nap and she had the biggest scratch on her cheek and it made me feel horrible. Her nails are super short right now so I’m not sure how she caught herself so hard. We’ve tried mittens but she always slips them off because she’s getting older and using her hands all the time.

What else can I do? When do they outgrow this?