there could be few probable reasons:

1) both of you are colleagues (same dept? team? floor?). so if there's a romantic r/s going on, it'll be very well "known" in the office. the girl may not want that attention. so handle this with care, professionally (in office). keep neutral for the time being until she is ready to commit further. subtle hint to her that office romance is not forbidden, just need to be careful.

2) as you mentioned above, "she have no experience how to date". this could be true. either she had bad r/s before this or she never dated anyone. you're currently taken a step back, which is a good sensible thing to do. dont scare her too much, just a little tease here n there should keep the momentum rolling. she's now easy and not feeling awkward, so that's a good start. keep is slow n steady!

3) constantly chatting with a "guy". ermmm yeahhhhh girls no need to overthink this portion, although you cant help to think THAT other guy. until she tells you she's into another guy, you're probably (temporary perhaps?) friendzoned by her. again, keep it stead and observe. she may be using this tactic to test you? or perhaps to make you jealous? to see/know if you really care for her, unconditionally? keep doing what you're doing with her. action speaks louder, so subtly engage with her as a close friend/colleague. she need someone but she may not aware of her feeling or even aware of YOU as a potential partner. proof her wrong!

4) seriously, she may not be single. LDR with her bf? or got a bf but not telling. some girls really do that. keeping her options open or dont want to be "branded" as someone's gf. still, keep the r/s as is. no need to over-chase her. since you both always hang out during lunch, trick her to confess! tai-chi this to her friends till she cant keep it a secret anymore. that'll be a good sign to you whether you should proceed or stop (unless you're a spanar).

regardless of her "status", if you really like or love someone dearly, you'll cherish her dearly. you may not be fated to be with her, for now. loving someone from afar is hurt/confusing/killing you inside-out but that's what unconditional love is all about. be happy that you have someone to love, hope she'll be happy, safe, and healthy.

keep observing and be patient.

well, that's my exact situation & intentions now all i can do is stop going after her and leave it as is (stay neutral and try detach any feelings/crush). i've tried various subtle intentions but almost no response, so I just know it wont go anywhere. why push is that far if the signs are not there?

anyways, moving on.......

interesting girl

but guess she's teasing you. but for what reason, no idea.

Plant, try not to totally ignore her. just normal casual interaction is enough. they are sensitive creature anyway.

suggest you continue as normal but once a while hint to her that she's giving signals that bothers YOU. if she play dumb-dumb what signals, then you confront her mildly, saying her signals are as if she's interested with you but you're confused

no harm be upfront once a while too. see her reaction if she's serious to spend time with you and considering to go further, OR she's just plainly like to play/tease you.

no ler, not that desperate

thse girls some of them are mostly probably established/stable (career, financially), so not rushing oso.

at this stage, the dating period could be shorter (1yr perhaps), instead of 2-3 years for younger couples.

1yr, imo, is enough to know the person, the bad and the worse. the personality, habits, behavior, family n friends, etc.

couples at this age range also more willing to share than hiding/secrecy cuz these "games" will prolong the relationship, and they are not willing to waste time doing so

^ hell yeah!

TS, you've done your part. it's up to her to decide and behave accordingly. the girl confusing you only

continue your work, work harder, proof her that you're awesome and great in the office. with or without her, you're still a great person. if she couldnt see past that, you've gotten the answer.

finally she showed her own stripes.

continue ignore her as usual. as the comments above, let her do what she want, without you being part of it.

good that you're "spared"

even if big misunderstanding, she shouldnt be too clingy with you at the first place. i'm sure being normal casual friends is ok, but the way she "stick" to you is borderline scary