If she fails to make mortgage payments, let alone permits the house to go into foreclosure, that may constitute grounds for ejectment proceedings on the basis of waste. (That is, should she put the property at risk by not fulfilling her legal duties, you may have a basis to terminate her life estate and evict her from the property.) But assuming the payments are actually made, her whining and threatening to miss payments are annoyances, not a basis for legal action.