Can a sick woman delay Fajr Prayer until 6 AM because of using vaginal suppositories and cream that prevent her from moving and performing the prayer on time?

If it is not possible to administer the treatment at another time, there is no harm in performing the prayer in a state that does not invalidate the treatment. You should do what you are able to do, and what you are unable to do, or what would spoil the effect of the medication, is waived for you. Do not delay the prayer beyond its prescribed time. It is permissible for a sick person to pray while lying down for treatment, based on the statement of a trustworthy Muslim doctor, because the Prophet (peace be upon him) "prayed sitting when his side was injured," either due to hardship or due to the presence of harm.