The Akadema Fastpitch Series: ANF71 First Base Mitt features a 12.50 inch pattern. For a player between the ages of 8-10 this may be a little big (recommended length would be 12.25 inches). For infield purposes, a glove from 11.50-11.75 inches would work best. At this time, the closest option within the Akadema lineup would be the Akadema Fastpitch Series: AJB74.
Based on your daughter's size we advise going with the Akadema Fastpitch Series: ANF71 First Base Mitt.
This Akadema Fastpitch Series (ANF71 First Base Mitt) will come with a 12.5" length and for a 16 year old firstbase lady, I think that length will work just fine for her. However, all gloves from JustBallGloves come with a 100 day guarantee. You would be able to get this glove and use it and if you decided to send it back under the 100 days, you would be eligible to get a full refund or exchange when we received it back.