How does a colon patient who suffers from continuous gas and forgets the number of Rak'ahs, prostrations, and Surahs perform ablution and pray, and is it permissible for her to combine prayers?

What you experience concerning the emission of wind has two situations:

The first is that its emission is not frequent, allowing you to pray with a valid state of purity. In this case, both ablution and prayer are invalidated by the emission of wind.

The second is that its emission is so frequent that you cannot find time to pray without wind being emitted. In this case, you are afflicted with chronic wind ( سلس الريح). Those afflicted with chronic incontinence have specific rulings mentioned in Fatwa (definition) No. 110540, which include the permissibility of combining two prayers.

As for doubting the number of rak'ahs, one should build upon the lesser number and perform the prostration of forgetfulness ( sujūd al-sahw) before the taslīm.

Regarding forgetting Al-Fātiḥah: if it is forgetting its recitation, then the prayer is not valid without it, and the rak'ah in which it was forgotten must be repeated. If it is forgetting its memorization, then a substitute from the Qur'an should be recited. If one does not know anything from it, then one should recite dhikr such as " Subḥān Allāh wal-ḥamdu Lillāh wa lā ilāha illallāh wallāhu akbar wa lā ḥawla wa lā quwwata illā billāh " (Glory be to Allah, and praise be to Allah, and there is no god but Allah, and Allah is the Greatest, and there is no might or power except with Allah).

If the questioner is suffering from waswasa (obsessive whispering), she must ignore doubts and not interrupt her prayer because of them. She is advised to fear Allah and not succumb to waswasa.