From the photo I would say female but it would be good to get photos from the side and from above to be sure. How old is your axolotl?
Does she have dark tips to her toes? That's an indication of sexual maturity and would mean that you could be positive that it's female. If no dark tips then there is still time to change.
Have a look at the information in the link.
Axolotls - Biology
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