It may not have anything to do with side effects of Citalopram, there are high statistics of women who have low sex drives, or who have come to the conclusion they do not enjoy, or cannot feel during sex. Women typically respond differently than men during sex through emotion. Whether it is caused by symptoms of the medication, there is nothing you can do unless you are her psychologist and she is abiding to it.
If you want to help her, perhaps put more effort out into turning her on, obviously what you are doing is not working, the woman is not broken, she needs more in order to feel more. You have already figured out that the emotional part of it helps her out, so use it. Instead of sticking to what usually works for you, try and get her into a hot emotional state and see what happens.
In most cases, when a woman does not feel much during sex, it is because they are not turned on enough, and also because they have not explored their own bodies enough to know what gets them off. Random sex does not cut it, a woman's body is very complex.
Women who know how to pleasure themselves, are those who have explored their bodies through masturbation, are open to new possibilities, and try different things. If you just stick it in and go at it, you are ruining the experience of allowing her to explore different things through penetration. There are so many different angles, positions, strengths, and several different patterns of thrusts you can use to get her off. For example on a downwards angle, the penis will rub against the g spot. A woman can orgasm in so many different ways, she just has to figure it out. It is pretty impossible for you to do that for her if you have no clue what she would like. It's not that a woman can't feel, it's just that they haven't learned how to yet.
For example, i can orgasm simply by feeling the intense electricity going on, or by looking at his facial expressions, what i feel emotionally would make a man jealous that he can't orgasm that way. I get off mostly when i see how into it he is, i like to please. But she may not be like that. You have to figure out what makes her tick. I used to have an ex, and i just liked to jump into it right away, but he insisted the best part of it was figuring out what each other likes, and he was right about that.
If you penetrate deeply, and hard, without moving out hardly, it creates a whole different female orgasm. If you do gentle surface penetration, without hardly going in, it is a whole different orgasm. You can come up with lots of combinations, to see what she can learn to feel, a woman can feel in a whole variety of ways.
It sounds like you need to be more compassionate, she needs passion, she needs to know you care, instead of using her like an object for pleasure, and THAT is what will make her orgasm, if she feels that expectation in the air, no wonder she doesn't want to. Seems like you probably put too much pressure on her, and ruin the fun of the experience. Try different ways of foreplay, not just jumping into sexual foreplay. Change up the environment. Change up your tactics. Maybe secretly she gets off on dirty things in public places, just an example, try to find her secret fetishes. Fire her up, and she will feel that need to have sex. She's not broken, she is normal, you just have to learn how to use it. Of course she does it to be close to you, so be close to her as well.
Celexa can definitely delay or dampen sexual response, and if she needs the Celexa, she needs the Celexa. If you want, you could try a "toy," which might give her an orgasm too. But if she is experiencing a lowered sexual thermostat, it is not like she is sitting around feeling horny and wishing she has hot sex and that you could figure out some magic way to give her an orgasm. In other words, if Celexa has this effect, it is not like she is frustrated. All you really can do is adapt your expectations. In other words, accept her medical reality and the side effects of what she is taking, stop being anxious over her performance, enjoy what you two can do sexually, and relax. She's not judging you, probably just wishes it would not be so important to you that she "feel more."