This is a very good question to ask. Of course, the way in which Mrs. Dickinson responds to her son when he cries and her embarrassment, mortification, and desire to distance herself from such unbridled demonstration of emotion is something that would cause us to question whether or not she actually loves him at all. Note what she says to her son when he starts to cry:
She whipped out a handkerchief and dabbed at him with it under his grey felt hat, exclaiming meanwhile in tearful mortification, "You really haven’t got to be such a baby!"
However, before jumping to such a conclusion, we need to be very careful that we understand her character and in particular the information we are given about her background and what happened to her during and after her husband's death. Let us remember that Mrs. Dickinson was able to remain "unnaturally" calm during and after her husband's death, but the only time she did cry was the first time she saw Frederick again after her husband had died. Clearly, we can see from this that she does love her son deeply, but she has repressed her emotions to such an extent that she is not able to cope with such a free expression of sadness. What we see in Mrs. Dickinson is somebody who has detached herself from her emotions to such an extent that she is unable to understand her son and needs to distance herself as a result. She still loves him, however.