What is the ruling on making up the fast for someone who masturbated during the day in Ramadan out of ignorance? And is it obligatory to make it up before the next Ramadan? And is it permissible to combine the intention of making up (a fast) with observing a supererogatory fast? And does repentance erase the sin of missed prayers and days of fasting?

The questioner must make up the prayers she missed. As for fasting, there is a difference of opinion regarding it, but the more preponderant view is that making it up is not obligatory. However, it is more cautious to make it up before the next Ramadan begins. It is permissible to fast on Mondays and Thursdays with the intention of making up (the missed fasts) to gain two rewards.