Who/What Is the woman that Watanuki meet in episode 22-23?

Question

1. In xxxHolic S1E22-23, Watanuki met a woman and it harmed his health. I just wonder if that woman is actually Watanuki's mother?

2. Why didn't Watanuki meet/attract any other spirit/ghost when he encountered the woman? Is the woman indirectly protecting Watanuki from harm from any other spirit/ghost?

3. Why was Domeki able to see the woman? Domeki is often not able to see or hear spirits/ghosts in earlier episodes when Watanuki could. Does it mean the woman is not a bad or "ill intent" spirit/ghost? Because Domeki is able to see Zashiki Warashi, Pipe Fox, Ame Warashi and other spirits in the Demon Parade (Episode 18) etc.

Answer 1

That woman is not Watanuki's mother. It is obvious from these episodes that Watanuki views the woman as a substitute for his own mother, and that the woman views him as a substitute for her son For instance, in volume 6, the woman says

I wanted to do this with my son but he passed away quite a while ago. If he'd been allowed to grow up, he might have become a nice boy like yourself.

Watanuki and the woman are not related, and this shows in their dialogue. Watanuki doesn't recognize the woman, and she specifically says her son passed away. They each know that the other is not their mother/son, but they've both lost loved ones, and they seek each other's company to try and fill that void, both for their own sake, and the other.

As for not encountering any other spirits, Watanuki goes for long periods of time without encountering any in the manga, so it really isn't that unusual. This is especially true after he begins associating with Domeki, who repels spirits. From a story perspective, each spirit encounter tends to be focused. The spirit Watanuki is encountering right now is the woman, so other spirits would only be included in the encounter if they are relevant.

And lastly, for Domeki being able to see the woman, I have no answer. I do not think the manga actually offers an insight on why some spirits can be seen by everyone and others cannot. If it does, it would be difficult to glean. Given how difficult it would be to analyze and answer this part, I believe this needs to be asked as a separate question, which I see you have already done here: Why can Domeki sometimes see Ghost/Spirit?

Later on in the manga, Watanuki's mother is revealed; however, this is a very big spoiler for both Tsubasa and xxxHolic, so please be wary of reading further.

Watanuki was created when the real Syaoran from Tsubasa made a wish. Watanuki is basically a clone of Syaoran. Thus, Watanuki considers his parents to be Syaoran's parents. This is why it is significant that Syaoran and Watanuki share a birthday (also, Sakura, but that's not relevant here).

Continuing on, there's an even bigger spoiler.

Watanuki and Syaoran's parents did not die in a car crash. They are still alive. This is stated in xxxHolic. The fortune teller from earlier in the series comes to Yuko to correct her statement that Watanuki's parents had moved on, saying she was mistaken, and they were merely far away and unable to come to him.

Here's the biggest spoiler of all. Seriously, if you are planning on finishing xxxHolic and Tsubasa, don't read this.

The real Syaoran's (and by extension, Watanuki's) parents are the fake Syaoran and fake Sakura. This is done via time looping. Fake Syaoran and fake Sakura end up dying, but Yuko grants them a wish to reincarnate as real people, which they do, in the past. You can see this in volume 28 of Tsubasa.