Mi amiga es capaz de subir diez pisos sin ascensor.

Es capaz de + infinitive literally means “is capable of” or “has the capacity to.” It often emphasizes someone’s potential or ability under challenging circumstances.
Poder + infinitive (for example, puede subir) simply states “can” or “is allowed to”, and is more neutral.
Example comparison:

• Ella es capaz de correr un maratón. (She’s capable of running a marathon—emphasis on capacity.)
• Ella puede correr un maratón. (She can run a marathon—neutral statement of ability.)

When you directly specify a quantity in Spanish, you usually omit the article.

• diez pisos = “ten floors” without an article.
  If you wanted to say “the ten floors,” you’d need an article: los diez pisos.

Here subir takes diez pisos as a direct object, meaning “to climb/go up ten floors.” No preposition is needed.
If you specify a destination rather than a number of levels, you use a:

• subir a la azotea (to go up to the rooftop)
  But for counting floors, it’s simply subir + number + pisos.

After sin (meaning “without”), Spanish normally omits the indefinite article when talking about lacking something in general:

• sin ascensor = “without an elevator.”
  You can say sin un ascensor if you want to stress “without a single elevator,” or sin el ascensor if referring to a specific one, but the bare noun is most common for general absence.

In Spain ascensor means “elevator.” Common regional variants include:

• Latin America: elevador
• Formal/technical: montacargas (usually for freight)
  Remember, escalera mecánica = “escalator.”

Yes, Spanish allows some flexibility, but word order affects emphasis.

• Original: Mi amiga es capaz de subir diez pisos sin ascensor. (neutral)
• Fronted: Sin ascensor, mi amiga es capaz de subir diez pisos. (emphasizes lack of elevator)
• Mid-sentence: Mi amiga, sin ascensor, es capaz de subir diez pisos. (more literary or formal)

Yes, you can say Mi amiga puede subir diez pisos sin ascensor, and the core meaning stays the same.
Nuance:

• puede = straightforward “can.”
• es capaz de = highlights capacity/potential, sometimes implying effort or overcoming difficulty.

In Spain, piso can mean both “floor” (story of a building) and “flat/apartment.” Context tells you which:

• subir diez pisos → floors
• alquilar un piso → apartment

Spanish nouns and adjectives agree in gender with the person they describe.

• A female friend is mi amiga.
• A male friend would be mi amigo.
  Always match -a for feminine, -o for masculine (and watch out for irregular endings).