"That girl is standing on a chair."
Translation:वह लड़की कुर्सी पर खड़ी है ।
No. Firstly, खड़ी is an adjective so you need to combine it with the verb होना to make it a verb.
'Stands' would be खड़ी होती है
One might think that 'खड़ी हो रही है' would then be 'is standing' but it is not so. It actually means 'is standing up', i.e, 'is in the process of standing up'.
खड़ा is more a run-of-the-mill adjective rather than being a participle. It is not derived from a verb. Rather, the verb form खड़ा होना (to stand up) is derived from the adjective.
बैठा is more like a participle. It is the perfect-tense form ('sat') of the verb बैठना (to sit down) but is used as an adjective.