if you are married and living together, and filing as Married filing separately, either of you may claim the child. You are not locked into who claimed him last year.
Yes, they will take everything from her separate return. There is no allocating of her refund, based on the child based credits or deductions.
You can file as Married Filing Jointly, and submit form 8379 , injured spouse allocation, to keep them from taking your refund to satisfy her debt.
