Oh the monsters. We also went through this with our daughter around 2 1/2-3 years of age. She is now 4.
I think your remedy will depend on what you think your daughter will comprehend... meaning, if she can distinguish between real and pretend.
When we were going through the monster stuff, I researched to find helpful ideas. Some said not to "play" that monsters are real by using the spray because it only tells the child that monsters do exist. However, some moms swear by it. And some children are not able to understand real and pretend and need things like the spray.
Helpful suggestions I found that we used were:
*have your child draw a picture of what a scary monster looks like. Then talk about it and draw things on the monster that make it more friendly (bow in the hair, holding flowers, etc.) Change the image of what a monster is.
*talk to your child about how you (dad, older siblings, dog, etc.) are here to protect her from anything and keep her safe. Let her know that that is your job and you are very good at it (you are brave, strong, etc.) "They" also say not to tell your child that you are afraid of things as an adult but that you used to be until ______ (fill in the method you choose: you got your own monster spray, learned monsters are pretend, etc.) "They" say that children need their parents to be strong, brave people that will protect them, like super heroes... one day they will know we are not perfect! For now it is ok they think we are "perfect"...
*watch Sesame Street (or Monsters Inc.) and explain that the puppets are monsters! Most children do not make that correlation; once they have a different image of what a nice monster looks like, you can make signs to hang in your home that say things like "only friendly monsters allowed" (...but the sign, again, may tell the child that monsters are real... your choice!)
*play fun make believe games with her (grocery store, princess, etc.) and talk about how amazing our minds are that we are able to have so much fun playing make-believe. Then you can also talk about how are minds sometimes imagine things that are not as much fun like monsters.
Some of these ideas may be too much for your 2 1/2 year old... Things that REALLY worked were talking to our daughter and getting her to open up about what it was that was making her afraid (ie: scared of darkness because she couldn't see). We talked to her about distraction. Now when she is afraid, she knows that she can distract herself by thinking of her "happy places" (we talked lots about happy places. Hers were a REAL candyland, playing with her best friend, going to the beach, etc.). Happy places helped a lot at bedtime when we talked about having happy dreams a.k.a. thinking about her happy places as she drifted off to sleep.
Lastly, we let her read books in bed. Sometimes she looks at them for 5 minutes, some nights an hour. They have become like a security blanket. They make her sleepy and distract her from scary thoughts. We also of course use a night light and keep the hall light on.
Let her know it is ok to be afraid and that you will always be there for her. (I know this is an exhausting stage! But it passes!) As long as she knows you understand, don't force her to be alone when she needs your safety and protection, then she will come out on the other side of this!
ALL children go through this! It just takes a lot of extra time, patience and understanding from the parents... just like any other stage: pacifiers, potty training, sharing, etc.
Hang in there! One day you will be able to use the bathroom independently once again!