I have similar situation with you. I am now nearly three months' pregnant and have a son of nearly 4.
I am also suffering from morning sickness and my son always asks me to play with him after I go home from work.
Yes, it is a very difficult period now because we are in a bad condition. However, for most of the case, morning sickness will pass after three months. You only have one more month to overcome. You have a maid to help you for six days a week. You only have less than a day to look after your daughter.
When I was very uncomfortable and could not play with my son, I would tell him the case and ask my maid to put down her work for the time being and play with him. You should emphasize that you are not ignoring her but just too sick to look after her. Children usually need someone to play with them and my son accepts the arrangement.
Have you discussed the issue with your husband? What's his response?
Don't give up. It's a life. The situation will be better.
Morning sickness is common and it will be over later.
But may I know why you are not dare to inform your relatives and friends about this? Yes, I can understand sometimes man cannot exactlly help you so much. But I think others can share with you at least mentally if you can inform them . Also, try to share your feelings with your husband and let him take care of or be patient to your daughter much more ....