In the situation you provided, I would not use that phrase construction, as likely to… as…, because it usually implies equal chance of two reactions in response to a single event.

If Mary sees a particularly embarrassing moment from a childhood video, in that situation she might be “as likely to laugh as to cry.” If I say two responses one after the other–if at first she starts to laugh and later begins to cry…then her response is not related to the likelihood of one event in a person’s life. What is the key or method of responding to her question?

How do you answer a question that really depends on the meaning of “changeable”. If you mean variable in temporal sense (that is, that the reaction changes in time), that the person’s reaction could change, then the phrase does not apply.

In the situation you provided, I would not use that phrase construction, as likely to… as…, because it usually implies equal chance of two reactions in response to a single event.

If Mary sees a particularly embarrassing moment from a childhood video, in that situation she might be “as likely to laugh as to cry.” If I say two responses one after the other–if at first she starts to laugh and later begins to cry…then her response is not related to the likelihood of one event in a person’s life. What is the key or method of responding to her question?

How do you answer a question that really depends on the meaning of “changeable”. If you mean variable in temporal sense (that is, that the reaction changes in time), that the person’s reaction could change, then the phrase does not apply.