Based on the text, what does Katrin's mother suspect about Frank's motives for not wanting Katrin to go to Prague?

Mother's Suspicion:

• Katrin's mother believes Frank's demand that Katrin not go to Prague is unfair.
• She suspects that Frank wants Katrin to be exclusively available for him, implying a possessive or selfish motive.
• The mother suggests that Frank might be testing the strength of their friendship by making such a demand.

Summary: Katrin's mother suspects that Frank's demand stems from a desire to monopolize Katrin's time and attention, indicating that he wants her to prioritize him above all else.