She probably still fits fine in her infant carrier, until her head reaches the top (when she is pulled down sitting nappy to buckle) or she maxes out the weight limit, whichever comes first.
Are you thinking of rear or forward forward facing? She needs to be rear facing until she is over 9kg, or until 15 months if you have an i-size seat. Safety rcommendations are rear facing until age 2, or ideally age 4 but legally its 9 kg or 15 months (2 laws running side by side atm)
Spin seats have a rear facing weight limit of 18kg (average age 4), so depending on the centiles of your child, she may outgrow it earlier. I'm not sure if the weight limit is different if forward facing, worth checking.
Extended rear facing seats generally have a weight limit of 25kg, but there are no spin versions.
I'd keep her in her infant carrier as long as possible. It doesn't matter if her feet touch the rear seat, this isn't an indication that she needs a bigger seat. We kept our LO in his infant carrier until I think around 10 or 11m, then moved him into an Axkid Minikid which is rearfacing until 25kg. Other plus tested extended rear facing seats are the Axkid Move, Britax Multitech, Britax Maxway Plus.
When looking for car seats I'd check out if they are plus tested, and ADAC testing reports.