What do you advise someone who suffers from depression and finds it difficult to perform prayer, while feeling regret and fear of falling short, and having suicidal thoughts, yet desires to maintain her prayers and her relationship with God?

A servant finds happiness and comfort only in obedience to Allah. Sadness and worry result from being far from Allah, as confirmed by His saying: "Whoever does righteousness, whether male or female, while he is a believer - We will surely cause him to live a good life, and We will surely give them their reward [in the Hereafter] according to the best of what they used to do" (An-Nahl: 97). What you feel, this reluctance to pray, is a whisper from Satan. You must strive against yourself and not surrender to him, for Allah has promised guidance to those who strive, as He says: "And those who strive for Us - We will surely guide them to Our ways" (Al-Ankabut: 69). Increase your supplications for guidance, associate with righteous people, listen to beneficial lectures, and remember the seriousness of abandoning prayer.