It is Permissible to delay making up missed Ramadan Fasts until before the next Ramadan comes, and this is for those who broke the fast for a reason such as sickness, travel, menstruation and the like Sahih Muslim 1146 e
Translation
'A'isha reported
If one amongst us had to break fasts (of Ramadan due to natural reasons, i. e. menses) during the life of the Messenger of Allah (ﷺ) she could not find it possible to complete them so long she had been in the presence of Allah's Messenger (ﷺ) till Sha'ban commenced.