It's not ungrammatical but it's not very meaningful to be hopeful of a person without further context. You can be "hopeful of" a future thing or situation. Here are three real sentences from fraze.it:
Now he has made the breakthrough, he is hopeful of making a more regular impact. (open, save, copy)
We received a good hearing and are hopeful of a quick response to this question. (open, save, copy)
The injured Williams said yesterday that she was hopeful of playing in the Open. (open, save, copy)
An easier construction to master is: hope to + verb e.g. She hopes to play in the Open.
If the person who hopes is different to the person who will do or is doing something, then you need
I hope that ... she is playing in the Open / she will play in the Open.