This sounds like two separate issues. One stealing, two food/toy aggression.

With stealing its about stopping the behavior before the are successful. Its hard for me to completely advise without seeing the behavior. But with our female when she starts making a move( watch for the signs) for our food or things she is placed in her kennel. This takes consitancy and time but she eventually associates that behavior with being excluded from the pack. But I will say it has not been easy, Basenjis can be sneaky and persistent.

Food aggression is tough. Its sounds like you have passed the point where you can rely on confidence of taking the food/toy without it getting serious. I would suggest making it a positive experience to deescalate the situation. Offer food or a toy enchange for what she has. If she has successfully stolen the food she thinks the food is hers. She will learn you are not always trying to steal from her. She won't get so aggro about it over time and you can work on it without an exchange. I would also highly reccomend doing this when she has something that is hers, its about her realizing that you do not always take things from her in negative situations.

Good luck.