Is it obligatory to return the money to the father that was spent claiming illness, or is repentance sufficient due to the inability to return it?

The questioner must repent from lying and harming her father. As for the money her father paid to the doctors, she is not obligated to guarantee it because the one who directly spent the money was the father, not her. When both a direct actor and an instigator are involved, the ruling is attributed to the direct actor. This is different from a situation where she had directly taken money from her father for treatment while lying, in which case she would be obliged to return it.